1. Field of the Invention
This invention relates to a magnetic transfer apparatus for magnetically transferring information on a master information carrier to a slave medium.
2. Description of the Related Art
In the magnetic transfer, the magnetization pattern representing the information (e.g., a servo signal) carried by a master information carrier is transferred from the master information carrier to a slave medium by applying a transfer magnetic field to the slave medium and the master information in close contact with each other, as disclosed, for instance, in Japanese Unexamined Patent Publication Nos. 63(1988)-183623, 10(1998)-40544 and 10(1998)-269566.
When the slave medium is a disc-like medium such as a hard disc or a flexible disc, a disc-like master information carrier is brought into close contact with one side or each side of the slave medium, and a transfer magnetic field is applied to the slave-medium-master-information-carrier assembly by a magnetic field application device disposed on one side or each side thereof. The magnetic field application device may comprise either an electromagnet or a permanent magnet.
In order to improve magnetic transfer quality, it is required to bring the slave medium and the master information carrier into a contact with each other as close as possible. When the close contact between the slave medium and the master information carrier is not satisfactory, information cannot be successfully transferred from the master information carrier to the slave medium, and local drop out occurs in parts where the information is not transferred, thereby deteriorating the quality of the signal recorded on the slave medium. In the case where the signal transferred is a servo tracking signal, the tracking function is deteriorated and the reliability deteriorates.
In conventional magnetic transfer apparatuses, the slave medium is mechanically pressed against the master information carrier in order to bring the slave medium into close contact with the master information carrier. Further, there have been known a magnetic transfer apparatus in which the former is pressed against the latter by way of an elastic material. (Japanese Unexamined Patent Publication No. 7(1995)-78337) The mechanisms where the slave medium is mechanically pressed against the master information carrier are disadvantageous in that it is difficult to press the slave medium and the master information carrier against each other under a uniform pressure, though advantageous in that a larger pressure can be obtained.
Further, there has been known, as disclosed in Japanese Unexamined Patent Publication No. 2000-67433, a mechanism where air between the slave medium and the master information carrier is evacuated in order to prevent air from being trapped therebetween and preventing close contact of them. However, this cannot allow the slave medium and the master information carrier to be pressed against each other under a uniform pressure.
When a vacuum contact system, where a holder containing therein the slave medium and the master information carrier is evacuated so that the slave medium and the master information carrier are pressed against each other under atmospheric pressure uniformly acting on the holder from outside, is employed, a uniform close contact of the slave medium and the master information carrier may be easily obtained since the atmospheric pressure uniformly acts on the entire area of the holder.
However, even if such a vacuum contact system is employed, it is difficult to obtain a uniform close contact of the slave medium and the master information carrier over the entire area thereof unless the atmospheric pressure uniformly acts on the entire area of the slave medium and the master information carrier through the holder. In order for the atmospheric pressure to uniformly act on the entire area of the slave medium, it is required that the slave medium and the master information carrier are highly flat and the upper and lower parts of the holder are highly parallel to each other. In the case that the holder is rigid, it is difficult in view of the quality control to constantly obtain such a high accuracy holder and it is disadvantageous in view of the cost to constantly obtain such a high accuracy holder. Unless the slave medium and the master information carrier are highly flat and the upper and lower parts of the holder are highly parallel to each other, the slave medium and the master information carrier cannot be uniformly in close contact with each other and local drop out can occur.